Medical devices such as catheters, wire guides, cardiac leads and the like have long been used to treat and improve the health of patients. Unfortunately, these devices occasionally break, fracture or fragment during use. Once broken or fragmented, a piece of a device can be released into the vascular system or elsewhere in the patient, even from such simple procedures as intravenous infusion or intravenous pressure monitoring. Any foreign body in the bloodstream has the potential to cause a number of clinical complications, including sepsis, perforation, thrombosis, arrhythmia, myocardial necrosis, and on occasion, even death. When such risk is encountered, it is urgent and vital to remove the foreign body from the patient, and a variety of approaches are known for such removal.
For example, open surgery is effective for removing a foreign body or article from the vascular system of a patient. Open surgery for this purpose is subject to numerous drawbacks, however. Open surgery is costly, is traumatic to the patient, requires long periods of patient healing and recovery, and entails its own risks of further complications. These risks are disproportionate to a patient who has only undergone a routine, noninvasive vascular access procedure.
Retrieval devices for removing a foreign body or article can be effective when employed in minimally invasive vascular access procedures. These procedures are typically performed with a visualization aid such as fluoroscopy, and several devices are known for this use.
For example, one known retrieval device has a distal hook. The distal hook is positioned centrally along the length of an elongated fragment or foreign body, and is pulled so as to drag the fragment through the vascular system and out of the patient's body. The use of such a device is subject to several drawbacks, however. The hook is unable to engage and pull a fragment or foreign body that is relatively short. Moreover, when the hook does engage the foreign body, the hook grasps it in a transverse orientation with respect to the axis of the retrieval device. As a result, the body extends from the hook at an angle, which makes it difficult to manipulate the hook and body through the tortuous vessels of the vascular system. The transversely extending foreign body can potentially stretch or catch on blood vessel walls and traumatize them. A further drawback of the hook type of device is that the elongated fragment or foreign body trails the hook in a doubled strand during travel through the tortuous vascular system. The fragment or body may cause significant drag or friction during removal, and since the hook lacks any structure to lock onto the fragment or body, the fragment or body may slide out of the hook, and again traumatize the blood vessel walls.
Another known type of retrieval device has a distal loop or snare which is positioned over a free end of the fragment or foreign body, and which is collapsed and tightened about it. One drawback to this type of device is that if the fragment or body is elongated, the snare grasps the fragment or body transversely with respect to the axis of the retrieval device. As with the hook type retrieval devices, the snare presents the fragment or foreign body transversely to the blood vessels through which it is pulled, potentially traumatizing the blood vessel walls. Further, the fragment or foreign body can become caught or wedged in the tortuous vessels and require surgical removal. Another problem with a distal loop or snare is that the wire making up the loop or snare can be easily kinked during introduction into the body, or during engagement with the fragment or body. Kinking often renders the snare ineffective, so that the snare must be replaced.
Yet another known retrieval device has a pair of distally positioned forceps jaws for grasping the fragment or foreign body anywhere along its length. One drawback in the use of jaw type devices is that the narrow, tortuous vessels of the vascular system offer limited space for the forceps jaws to open and close. Moreover, when the fragment or body is elongated, the jaws are typically used to grasp its central portion. As a result, the fragment or body has a transverse orientation with respect to the axis of the retrieval device, and encounters the same potential for traumatizing blood vessel walls disclosed above. Inadvertent release of the fragment or foreign body is also possible.
Several specific devices address some but not all of these problems. For example, the transverse positioning of the engaged fragment or foreign body is obviated in the helical snare disclosed in U.S. Pat. No. 5,342,371 (Welter et al., Aug. 30, 1994). That snare includes an elongated tubular member, and a filament wire exiting the member through inclined side ports, the distal portion of the wire being wrapped about the distal portion of the member. The wire forms a helical snare loop externally around the tubular member, which traps an elongated fragment or foreign body against the tubular member in an orientation parallel to it.
As additional examples, the kinking of a snare loop can be obviated by the use of a shape memory material for the snare, as in U.S. Pat. No. 5,201,741 (Dulebohn, Apr. 13, 1993) or U.S. Pat. No. 5,171,233 (Amplatz et al., Dec. 15, 1992). The best-understood shape memory material is the nickel-titanium alloy system known as "nitinol," which exhibits superelastic properties when maintained at a temperature above its transition temperature. The snares of the reference devices are composed of nitinol wire having a transition temperature below the operating temperature of the snare, for example, below body or room temperature. This allows the snares to be manipulated in relatively severe manners during introduction into the patient, but to recover their desired shapes (without kinking or other deformation) after such manipulation.
While neither reference addresses the problem of transverse orientation of the engaged fragment or foreign body, the device of Amplatz et al. does orient its nitinol loop at an angle with respect to an elongate proximal member on which it is carried. The loop of the Amplatz et al. device is provided with a small U-shaped arch at its distal tip to make it easier to insert the snare into the catheter which introduces it into the patient. The loop and distal tip preferably lie generally flat in a single plane, but the major axis of the loop may instead be curved. The specific utility of the curved loop does not appear to be expressly stated in the patent; however, since the purpose of the angle of the flat loop is to enhance the ability to slip the loop over an end of the foreign body to be retrieved, it can only be presumed that the purpose of curving the loop is also to facilitate slipping the loop over an end of the foreign body. There is no disclosure or suggestion that the curved loop of the Amplatz et al. device is intended to, or even can, function in the same way as the hook of the hook type retrieval devices mentioned above. Indeed, the superelasticity of the nitinol wire would appear to affirmatively prevent the curved loop from functioning like prior hooks. Accordingly, the Amplatz et al. device should still suffer some of the drawbacks associated with other snare type devices, most notably, that the snare loop must be placed over an end of the foreign body in order to engage it.